This invention relates to power amplifying devices, more particularly to a power amplifying device containing a differential amplifier and having a load in the form of a loudspeaker.
Usually in a power amplifying device which amplifies a low frequency signal for supplying its amplified output to a loudspeaker which converts it into a musical tone, such speaker driving characteristics as the damping factor etc., are improved by designing the output impedance of the amplifier to be as small as possible. However, even when the output impedance of the power amplifier is small, where the resistance of a line interconnecting the power amplifier and the loudspeaker is large, such large line resistance degrades the characteristics described above. However, in the prior art power amplifier, since the resistance of the loudspeaker connecting line has not been considered, when the length of the line is large, not only is the damping factor determined by the ratio of the impedance of the loudspeaker to the output impedance of the power amplifier decreased but also the frequency characteristic is degraded.